Cyrille Donlifack Atemkeng

From recent research, lignocellulosic materials assert themselves as good precursors for the manufacture of highly carbonaceous and porous materials. Hence, the perspective of this work is the preparation of the low-cost activated carbons (ACs) based on puck shells ( Afrostyrax lepidophyllus ) with a large surface area. To achieve this, chemical activation using phosphoric acid and sodium hydroxide as an activating agent was carried out. The response surface methodology through Box–Behnken design was used to optimize the preparation conditions. Box–Behnken design was used to optimize the preparation conditions. The factors whose influences have been studied are the concentration of activating agent (0.5–1.5 mol l ⁻¹ ), the carbonization temperature (300–500°C) and the residence time (30–100 min). The AC obtained by phosphoric acid was named CRP and impregnated with sodium hydroxide CRB. The ideal conditions for the preparation of the ACs obtained from the maximum iodine number (647.29 for CRP and 575.15 mg g ⁻¹ for CRB) were: 1.5 mol l ⁻¹ for the concentration of activating agent at a carbonization temperature of 500°C during 62 min for CRP and 0.85 mol l ⁻¹ for the concentration of activating agent at a carbonization temperature of 500°C during 59 min for CRB. These two materials prepared were characterized by several techniques pH at the point of zero charge (pHpzc), Boehm titration, Fourier transform infrared spectroscopy, XRD analysis, BET method, Raman spectroscopy and scanning electron microscopy, which confirmed the acidic nature of CRP and the basic nature of CRB carbons. The specific surface of the micropores was 509.05 and 27.53 m ² g ⁻¹ , respectively. It provides a new valorization of agricultural waste for the preparation of effective-cost microporous ACs as an adsorbent that can be applied in water treatment industries.

The interest of this work is to evaluate the possibility of using safou seeds to develop a new low-cost adsorbent and study its application to remove bisphenol A from an aqueous solution for a sustainable and ecological use of this biomass. This was done by optimizing some parameters that influence the adsorption process. The central composite design with four centre points was used to optimize the process variables. The concentration of bisphenol A solution, adsorbent dosage, stirring time, and solution pH on the adsorption capacity were considered, while the response measured was the quantity adsorbed. The activated carbon obtained by treatment with H₂SO₄ was named NSST and that obtained by treatment with H₃PO₄ was named NSPT. XRD revealed an amorphous character for the ACs, and EDXS showed they are mainly carbonaceous. Under the optimal adsorption conditions, NSPT showed the best performance. Correlation coefficients R² and R²_adj were of 85.13 and 69.12 for NSPT and 83.71 and 66.17 for NSST. A pseudo-second-order nonlinear kinetic model best described the adsorption kinetic of BPA removal by the ACs. Langmuirs isotherm best described the adsorption of BPA onto both adsorbents. Thermodynamic studies suggested an exothermic and physisorption process.

Two coordination compounds, copper (II) fumarate (CuFum) and copper (II) tartrate (CuTart), synthesized from copper (II) with fumaric acid and tartaric acid as ligands and using the slow evaporation method have been applied to study the adsorption of phenacetin in aqueous solution. These compounds were characterized by elemental analysis, IR-FT spectroscopy, and X-ray powder diffraction. The melting points of the synthesized coordination compounds were found to be above 350°C. The influence of parameters such as the initial pH, the contact time, and the initial concentration on the adsorption of phenacetin in an aqueous solution has been studied. The studies showed that adsorption equilibrium was reached after 80 minutes for both coordination compounds; the adsorption capacity increased with increasing phenacetin concentration, and the maximum adsorption capacity was obtained in the acidic medium at pH 4. The adsorbed amount of phenacetin on copper (II) fumarate (CuFum) was 25.158mg/g while that on copper (II) tartrate (CuTart) was 25.906mg/g. Nonlinear regression analysis showed the best fit for the Freundlich model isotherm for CuTart with R² of 0.963 and a Chi-square test (χ²) of 0.529 while for the CuFum material, it is the Redlich-Peterson model with R² of 0.975 and Chi-square test (χ²) of 0.263. The kinetic study shows that the pseudo-second-order model better describes the adsorption of the two materials. The results show that physisorption and chemisorption participate in the adsorption of phenacetin and that these materials can be used for the elimination of phenacetin in solution.

The present work demonstrates the adsorption of hydroquinone (HQ) and resorcinol (R) by activated carbon based on shea residue (Vitellaria paradoxa). The adsorbent was prepared chemically by impregnation with sulfuric acid and coded by the acronym CAK-S. The central composite design (CCD) was used to optimize the main factors that influence the adsorption of HQ or R by activated carbon such as the initial concentration, the pH of the solution, the contact time, and the mass of the carbon on the expected response, which is the adsorbed quantity of the target pollutants. The optimal conditions obtained from the statistical analysis are as follows: concentration of 158 mg/L, pH 3, time of 120 min, and mass of 50 mg for the adsorption of HQ and concentration of 180 mg/L, pH 3, time of 86 min, and mass of 118 mg for the adsorption of R. The maximum quantities of HQ and R adsorbed are 45.02 mg/g and 33.65 mg/g, respectively. The analysis of variance (ANOVA) showed a good relationship between the variables involved with the coefficients of determination R² = 98.69% for the adsorption of hydroquinone and R² = 90.55% for that of resorcinol, which means that the model is more suitable to express the adsorbed amount according to the four optimized parameters. The experimental data obtained under these optimal conditions were simulated with two and three parameter nonlinear isotherm models as well as kinetic models. The results show that Elovich kinetic model better describes the adsorption of HQ and R, indicating chemisorption with heterogeneous active sites on the surface of CAK-S. Temkin’s two-parameter model shows that adsorption occurs on heterogeneous surfaces with a nonuniform adsorption energy distribution at the surface and Sips’s three-parameter model confirms the heterogeneity of the surface with a localized adsorption of HQ or R by CAK-S. The thermodynamics study has shown that the adsorption is endothermic ( ) and spontaneous ( ).